Top-Gun

~3 years ago I removed my calipers to refinish/overhaul. When I did this, I used a line clamp to temporarily pinch each caliper line, removed the caliper, then installed a block off (made from an old set of lines) before removing the clamp. I wanted to keep the system full and sealed and the ABS pump full while the calipers were removed.

I tore the calipers down, inspected, glass beaded (with proper block off's in place), cleaned x 10, painted, and rebuild with OEM parts. I then reinstalled them and flushed the system via Motive bleeder using a couple cans of ATE super blue. At the time I achieved what I thought was a good bleed and the pedal felt good.

Fast forward a year and as part of annual maintenance I decided to check the brakes again, hooked up the Motive and surprisingly I found a few large bubbles and many microbubbles emanating from at least two calipers. I spent a good hour bleeding at this time, tapping the lines and calipers to release any trapped air.

Now just this weekend I decided to do another check while I was doing an oil change, and again I have bubbles coming out on the inner only of two calipers. I did a visual front to back and can't see any leaks, fluid level has never moved in between bleeds, and brake pedal has always felt fine.

Is it typical for air to be this difficult to remove from these cars? I don't have ABD but could it be air in the ABS pump that I didn't get as I never used a scantool to cycle the pump (despite not draining the pump)?

Thanks.

nine9six

When you bleed the brakes, are you using the wet or dry method? Are you also bleeding the clutch slave? Yes, I realize the clutch slave is somewhat separate but both pull fluid from the same reservoir.

What doesn't make sense, is that you are not complaining of a brake pedal that seems to get softer with time...Perhaps the brake master is inducing air into the system via a micro leak?

I am only aware of 2, maybe 3 diagnostic tools that are capable of bleeding the ABS and ABD systems. The Bosch hammer and the PIWIS. A PST2 may also be capable of cycling the system(s)... the ABS system is closed if not being actuated and therefore would not induce air into the system, especially between bleeds when the car hasn't moved!

You can also cycle the ABS in the wet, by slamming on the brakes and making the ABS system operate. Doing so in the dry, will unnecessarily abuse your tires.

NC TRACKRAT

You haven't specifically said that you have a soft pedal. If the pedal is firm then, in all probability, what you are seeing is air that is being induced right at the bleed nipple, not in the lines. Try keeping downward pressure on the nipple as you crack it open and only crack it open sufficiently to get fluid flow. See if that helps alleviate or eliminate the bubbles.

Grapeape

delete

Grapeape

Are bleed fittings on top of caliper?

Paddy

Remember each caliper has two bleed nipples.

pp000830

If your brakes feel good, the observed issue may simply be air introduced at the bleeder nipple and is of no consequence. If enough air was remaining in the system to produce several bubbles I would think you would have spongy brake peddle feel.

Top-Gun

Thanks for the replies. Bleeding was done via wet method, i.e. Motive with a half litre of fluid in it. Bleeders oriented at the top and both on each caliper were done. Clutch bled at the same time, was done first actually (highest/furthest point). I got air out of the clutch both times as well. Although the brake pedal felt fine, the clutch engagement point seemed to rise over time. Clutch master/slave/hose were all replaced when I did the calipers.

The suggestion of air at the bleeder is a good one, however in cases when bubbles appeared I was able to get bubbles multiple times (i.e. after filling the discharge line and cycling the bleed screw). It seems everytime I cracked it, more bubbles appeared, eventually tapering down to nothing.

On this last round I only got air from two calipers, and only from the inner halves of each. I'm stumped, I'm going to wait a few days and do one more bleed cycle.

PANHEAD201

Hi,
testing abs in a wet parking lot,you can hear and feel it. Do it twice,the second time keep your hands off the wheel. I've had to buy an Autozone vacuum pump for about twenty bucks.
Make sure the nipples are really clean. Put a little Vaseline on the bleeder nipples,and around the gasket on the vac pump reservoir. Pull the vacuum down to about twenty or 30lbs. If your vacuum drops you've narrowed it down. Having a firm pedal and no excessive pedal travel I can't think of anything else If you put new bleeder valves on when you did the rebuild if it was me I'd look for burrs, effed up threads,a dirty seat,etc. After I do one I'll run a tap down the holes. Ialways hone the cylinders,and measure the hole. I always put em back in the same holes they came out of. I use Loctite green sleeve retainer and thread sealersleer. Keeps em torqued but clean and I'll get em bright red.Heat doesn't bother it. I've never used clamps to pinch a line closed. Good luck and I hope you find it.If you've got a stiff pedal and no problems,I'd just drive it.